The objective of the proposed research is to investigate regulation of protein synthesis in cells treated with the antiviral agent interferon. Extracts prepared from interferon-treated cells have been shown to contain an enzyme activity which can be measured by passing the cell extract through a column containing poly(I).poly(C) bound to agarose. The enzyme binds to the column and is activated by the double-stranded RNA, so that addition of the proper substrate, ATP, to the column results in the formation of an inhibitor of protein synthesis. The inhibitor is a trinucleotide with a 2'-5' phosphate backbone (pppApApA). This trinucleotide activates an endonuclease present in all cells, whether normal or interferon-treated. We plan to investigate the role of the endonuclease in the establishment of the antiviral state. It seems possible that the synthesis of pppApApA can be localized in cells infected by viruses and treated with interferon at the level of replicative complexes of viruses containing dsRNA. We will attempt to isolate these complexes from virus-infected cells and to show that they contain bound pppApApA synthetase.